This is also really the truth of it. Legendary is the quality of the item and the amount of stats it has on it. It's much more about time consuming grinds than rarity. It's been that way since Shadowmourne. All the legendaries before that were just pure RNG drops which was the absolute worst design ever for the concept so there's no point even arguing about that.
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More people actually got Shadowmourne during Wrath than those that got Thoridal during TBC though. I'm not saying Shadowmourne was a good design either because it wasn't. MoP has been the absolute best Legendary the game has ever had in terms of being relevant for progression and being more than just a trophy you get afterward.